The invention relates to ultrasonic imaging systems for observing the distribution of ultrasonic sources as an image, or a series of such images, the sources being either emitters or echo sources with suitable projection or excitation.
For example, ultrasonic imaging systems for medical diagnostic use or industrial non-destructive testing have been, similarly to the RADARs or SONARs, constructed and used in the form of a so called "B-scope" to represent the target images for easy visual interpretation. A typical style of such a diagnostic ultrasound imager for real time monitoring is illustrated in FIG. 1. Using an array of small transducer elements (2) coupled to an object, i.e. human body (1), a series of narrow pulsed ultrasonic energy is projected into the object (1), and the echos from the target are received by the same array (2). Scanning is done by selecting or shifting the active element or elements within said array, and the echo intensity is displayed on a CRT screen (3) with the intensity modulation of a spot being deflected analogously in accordance with the sound propagation. A complete picture is constructed with a significant number of successive scannings, e.g. .gtorsim.100, the picture rate (or so called "frame rate") being practically limited by the propagating velocity of sound in the object space, i.e. in case of the human body nearly equivalent to that of water or about 1.5 Km/sec. For example, 100 scan lines for about 20 cm depth enables no more than about 30 pictures/sec., which is fairly marginal for detailed recognition for human sight without flicker. For these kinds of "line-serial" imaging schemes improvement on this sound velocity limited picture rate problem (in other words, line number vs. picture rate problem) has been limited, although inter-lacing techniques, multiple, simultaneous, transmission-reception techniques, or inter-line interpolation techniques, etc. have been proposed. In case of sector scanning with a high speed rotating transducer, or an electronic phased array method, the situation is essentially the same.
On the other hand, an omnidirectional transmission from point, line or planar source followed by reception with a similar array transducer enables a post-computation imaging scheme, but the requirements for computation speed and/or capacity for actual real time monitoring is still far from practical feasibility.